Process of producing a material having good spring properties

ABSTRACT

A process for treating nickel-copper alloys whereby the alloys attain corrosion-resistant and spring-like properties which comprises heat-treating the alloy to a temperature above 900*C; cooling the alloy to room temperature; cold-rolling the alloy; and tempering the alloy at a residence time of at least 1.5 minutes at 350* to 600*C.

i United States Patent 11 1 Wenderott Oct. 28, 1975 PROCESS OF PRODUCING A MATERIAL [56] References Cited HAVING GOOD SPRING PROPERTIES UNITED STATES PATENTS [75] Inventor: Berthold Wenderott, Winkelsen, 1,755,554 4/1930 Mudge 148/162 Germany 2,048,165 7/1936 Pilling et a1 148/162 2,102,238 12/1937 Pilling et a1. 148/162 1 Asslgneei Verelnlgie Deutsche Metallwerke 2,234,955 3 1941 Bieber et a1. 148/162 AG, Frankfurt am Main, Germany g ExaminerW Attorney, Agent, or Firm-Karl F. Ross; Herbert [21] Appl. N0.: 497,640 Dubno 30 Foreign Application Priority Data [57] ABSTRACT Sept 12 1973 Germany 2345882 A process for treating nickel-copper alloys whereby the alloys attain corrosion-resistant and spring-like [52] Cl u 148/115 148/12 148/32 properties which comprises heat-treating the alloy to a 14862 temperature above 900C; cooling the alloy to room [51] Int CLZ C221) 1 temperature; cold-rolling the alloy; and tempering the [58] Field of 32 alloy at a residence time of at least 1.5 minutes at 350 14 Claims, No Drawings PROCESS OF PRODUCING A MATERIAL HAVING GOOD SPRING PROPERTIES FIELD OF THE INVENTION The invention relates to a process of producing a spring material which has a high modulus of elasticity, a high limit of flexural elasticity, a spring characteristic which is stable at high temperatures, and a high resistance to corrosion.

BACKGROUND OF THE INVENTION So far, high-chromium steels, nickel alloys and the highly expensive copper-beryllium and copper-cobaltberyllium materials have been used as spring materials. These materials cannot always satisfy the often very high requirements. The copper-tin alloy CuSn which is also often used, has e.g., a modulus of elasticity of 1 1,700 kilograms per square millimeter and a limit of flexural elasticity of 40 kp (kilopound or kilogramforce) per square millimeter. The copper-beryllium materials can be used only in a few cases because they are highly expensive. They have a modulus of elasticity of 13,500 kp per square millimeter and a limit of flexural elasticity between 80 and 105 kp per square millimeter. These values at room temperature are in many cases still adequate. On the other hand, materials are increasingly required which have a spring characteristic that is stable up to relatively high temperatures. The conventional copper-base spring materials, such as copper-zinc and copper-nickel-zinc alloys, can be used only up to temperatures of l50200 C. The stainless and heat-resisting steels and the high-chromium nickel alloys have spring properties which are satisfactorily stable up to about 300 C. Only the highly expensive copper-beryllium materials can be used in continuous service at temperatures of 350375 C. without an appreciable change of their spring characteristic.

All known spring materials are more or less unsatisfactory as regards their resistance to corrosion. For instance, the chromium-alloyed steels and alloys are susceptible in the presence of chlorine ions to stress crack corrosion, which may have a disastrous influence on the fatigue strength of a spring.

OBJECT OF THE INVENTION It is an object of the invention to provide a spring material which has a particularly high modulus of elasticity, a particularly high limit of flexural elasticity and a spring characteristic that is stable even at elevated temperatures and which exhibits a high resistance to corrosron.

SUMMARY OF THE INVENTION It has surprisingly been found that this object can be accomplished where a nickel alloy, which contains -35% by weight copper, 36% manganese, 0.l-3% titanium, 0.1l.0% aluminum, 0.32.5% iron, with the balance nickel and impurities which are due to the manufacture, is subjected to a solution heat treatment above 900 C. before the last cold-working step, which amounts to at least 40%, and is tempered at 350-600 C. for at least 1.5 minutes after said cold-working step.

Under the same conditions, spring materials can be produced from nickel alloys which differ from the firstmentioned alloy in that nickel has been replaced in an amount of up to 10% by cobalt and/or in an amount of 2 up to 6% by iron. Besides, titanium may be replaced in the nickel alloy entirely or in part by zirconium and/or columbium. Finally, up to 2% chromium and/or molybdenum may be added to the nickel alloy.

In a development of the process according to the invention, a spring material having a modulus of elasticity above 15,000 kp per square millimeter, a limit of flexural elasticity above kp per square millimeter, a spring characteristic which is stable up to above 380 C., a high resistance to corrosion, and a good workability is suitably produced in that the nickel alloy is subjected to a solution heat treatment above 900 C., then quenched in water, cold-worked with a reduction of at least 40% in cross-section, and tempered at 350-500 C., preferably 400450 C., for at least 1.5 minutes.

To produce a spring material which has a modulus of elasticity above 18,000 kp per square millimeter, a limit of flexural elasticity above kp per square millimeter, a Spring characteristic which is stable up to above 400 C., and a high resistance to corrosion, it is preferable to subject the nickel alloy to a solution heat treatment above 900 C then to cool it to below 350 C. at a rate below 15 C. per hour, to cool it subsequently to room temperature, thereafter to cold-work it with a reduction of at least 60-80% in cross-section, and to temper it at 450-600 C., preferably at 500550 C., for at least 1.5 minutes.

If the articles to be made from the spring material are required to have optimum spring properties whereas a very high dimensional accuracy is less important, it is desirable in the last modification of the process to temper the material for at least 60 minutes. If it is essential, on the other hand, that the articles preferably strip, made from the spring material should be absolutely planar, the material is preferably tempered continuously with an effective residence time of l.55 minutes. For articles for which maximum spring properties are mainly important, the material is suitably tempered in a case-hardening furnace for 60-180 minutes. In other words, the residence time should range between 1.5 and 180 minutes.

The invention will be explained more fully with reference to the following examples.

EXAMPLE 1 For making highly stressed disc springs for use in chemical engineering, a spring strip was required which has dimensions of millimeters x 0.8 millimeter and the following properties (note kp=kg-f.=kilogramforce):

Modulus of elasticity Limit of flexural elasticity Spring characteristic is at least 18,000 kp/mm' at least 100 kp/mm stable in continuous service up to 450 C. Chemical resistance to fluids having a caustic soda content up to 20% 18,900 kp/mm 125 kp/mm" Modulus of elasticity Limit of flexural elasticity No change of spring characteristic during continuous service at 420450 C. for 500 hours. No appreciable wear by corrosion was noted during that time.

EXAMPLE 2 For miniature switching relays, a spring strip having dimensions of X 0.20 millimeter was required, which should have a modulus of elasticity of at least 18,000 kp per square millimeter, a limit of flexural elasticity above 90 kp per square millimeter, a spring characteristic which is stable up to at least 400 C. in continuous service, and a flex life of at least 5 (bend line at right angles to direction of rolling).

The same alloy was used as in Example 1 but the hotrolled strip was quenched in water from the rolling heat (above 900 C.) to attain the solution heat-treated state. The strip was subsequently ground and coldrolled to a thickness of l millimeter, which is 5 times its final thickness, and was then subjected to a continuous interstage annealing at 900 C. in a cracked gas and thereafter cold-rolled to a thickness of 0.2 millimeter. The strip was continuously tempered at 400 C. with a residence time of 2.5 minutes in the furnace.

All required spring properties were attained. The workability of the material when supplied to the final user was also satisfactory. Relays made from this spring material did not exhibit any variation after a functional test for 1000 hours.

It is apparent that the spring material made according to the invention is superior to the conventional spring materials in almost every respect. The material is inferior to the conventional copper-base alloy materials only as regards electrical conductivity and this is significant only with current-carrying springs. The electrical conductivity of the material according to the invention is of an order of O.81.2 m/ohm-mm'-, which corre' sponds to the values for stainless steels or highchromium nickel alloys. In special cases, in which a high electrical conductivity is required in addition to particularly good spring properties, the materials according to the invention may be coated with copper or silver by electroplating or cladding so that the resulting spring material according to the invention matches the conventional copper-base spring materials also as regards electrical conductivity.

1 claim:

1. A process for producing a corrosion-resistant, spring material which comprises the following steps:

a. solution heat-treating a body of an alloy which consists essentially by weight of:

25 to 35% copper 3 to 6% manganese 0 to 3% titanium 0.1 to 1% aluminum 0.3 to 6% iron 0 to 10% cobalt 0 to 2% chromium 0 to 2% molybdenum 0 to 3% zirconium 0 to 3% columbium with the balance essentially nickel at a temperature above 900 C.;

b. cooling the alloy body; c. cold-working the alloy body to reduuce its crosssectional area by at least 40%; and d. tempering the alloy for a residence time of at least 1.5 minutes at 350 to 600 C.

2. The process of claim 1 wherein the alloy is quenched in water in step (b).

3. The process of claim 1 wherein in step (b) the alloy is first cooled to below 350 C. at a rate of below 15 C. per hour, and is then subsequently cooled to room temperature.

4. The process of claim 1 wherein in step (d) the alloy is tempered for a residence time of from 1.5 to 5 minutes at 400 to 450 C.

5. The process of claim 1 wherein in step (d) the alloy is tempered for a residence time of 60 minutes at 6. The process of claim 1 wherein in step (d) the alloy is tempered by case-hardening for a residence time of from 60 to 180 minutes at 550 C.

7. The process of claim 1 wherein in step (c) the cold-working is accomplished by cold-rolling.

8. The process of claim 4 wherein the temperature is 500 to 550 C.

9. The process of claim 2 wherein the treated alloy has a modulus of elasticity above 15,000 kp/mm a limit of flexural elasticity above kp/mm and a spring characteristic which is stable up to about 380 C.

10. The process of claim 3 wherein the treated alloy has a modulus of elasticity above 18,000 kp/mm a limit of flexural elasticity above kp/mm", and a spring characteristic which is stable up to about 400 C.

11. The process as defined in claim 1, wherein in step (c) the cross-sectional area of the material is reduced by at least 60 to 80%.

12. A metal body consisting essentially by weight of:

a. solution heat-treating the body at a temperature 25 to 35% copper above C;

3 t0 6% manganese b. cooling the metal body;

0 to 3% titanium i c. cold-working the metal body to reduce its cross- 0 1 to 1% aluminum sectional area by at least 40%; and

' d. tempering the body for a residence time of at 0.3 to 6% iron least 1.5 minutes at 350 to 600 C. 0 to 10% Cobalt 13. The metal body as defined in claim 12 having a modulus of elasticity above 15,000 kp/mm a limit of flexural elasticity above 80 kp/mm and a spring char- 0 to 2% molybdenum acteristic which is stable up to about 380 C.

14. The metal body as defined in claim 12 having a modulus of elasticity above 18,000 kp/mm a limit of 15 flexural elasticity above 90 kp/mm and a spring charwith the balance essentially nickel treated by a proacteristic which is stable up to about 400 C.

cess which comprises the following steps:

0 to 2% chromium 0 to 3% zirconium 0 to 3% columbium 

1. A PROCESS FOR PRODUCING A CORROSION-RESISTANT, SPRING MATERIAL WHICH COMPRISES THE FOLLOWING STEPS: A SOLUTION HEAT-TREATING A BODY OF AN ALLOY WHICH CONSISTS ESSENTIALLY BY WEIGHT OF: 25 TO 35% COPPER 3 TO 6% MANGANESE 0 TO 3% TITANIUM 0.1 TO 1% ALUMINUM 0.3 TO 6% IRON 0 TO 10% COBALT 0 TO 2% CHROMIUM 0 TO 2% MOLYBDENUM 0 TO 3% ZIRCONIUM 0 TO 3% COLUMBIUM WITH THE BALANCE ESSENTIALLY NICKEL AT A TEMPERATURE ABOVE 900*C., B. COOLING THE ALLOY BODY, C. COLD-WORKING THE ALLOY BODY TO REDUCE ITS CROSS-SECTIONAL AREA BY AT LEAST 40%, AND D. TEMPERING THE ALLOY FOR A RESIDENCE TIME OF AT LEAST 1.5 MINUTES AT 350* TO 600*C.
 2. The process of claim 1 wherein the alloy is quenched in water in step (b).
 3. The process of claim 1 wherein in step (b) the alloy is first cooled to below 350* C. at a rate of below 15* C. per hour, and is then subsequently cooled to room temperature.
 4. The process of claim 1 wherein in step (d) the alloy is tempered for a residenCe time of from 1.5 to 5 minutes at 400* to 450* C.
 5. The process of claim 1 wherein in step (d) the alloy is tempered for a residence time of 60 minutes at 550* C.
 6. The process of claim 1 wherein in step (d) the alloy is tempered by case-hardening for a residence time of from 60 to 180 minutes at 550* C.
 7. The process of claim 1 wherein in step (c) the cold-working is accomplished by cold-rolling.
 8. The process of claim 4 wherein the temperature is 500* to 550* C.
 9. The process of claim 2 wherein the treated alloy has a modulus of elasticity above 15,000 kp/mm2, a limit of flexural elasticity above 80 kp/mm2, and a spring characteristic which is stable up to about 380* C.
 10. The process of claim 3 wherein the treated alloy has a modulus of elasticity above 18,000 kp/mm2, a limit of flexural elasticity above 90 kp/mm2, and a spring characteristic which is stable up to about 400* C.
 11. The process as defined in claim 1, wherein in step (c) the cross-sectional area of the material is reduced by at least 60 to 80%.
 12. A metal body consisting essentially by weight of: 25 to 35% copper 3 to 6% manganese 0 to 3% titanium 0.1 to 1% aluminum 0.3 to 6% iron 0 to 10% cobalt 0 to 2% chromium 0 to 2% molybdenum 0 to 3% zirconium 0 to 3% columbium with the balance essentially nickel treated by a process which comprises the following steps: a. solution heat-treating the body at a temperature above 900* C.; b. cooling the metal body; c. cold-working the metal body to reduce its cross-sectional area by at least 40%; and d. tempering the body for a residence time of at least 1.5 minutes at 350* to 600* C.
 13. The metal body as defined in claim 12 having a modulus of elasticity above 15,000 kp/mm2, a limit of flexural elasticity above 80 kp/mm2, and a spring characteristic which is stable up to about 380* C.
 14. The metal body as defined in claim 12 having a modulus of elasticity above 18,000 kp/mm2, a limit of flexural elasticity above 90 kp/mm2, and a spring characteristic which is stable up to about 400* C. 